An article in Newsweek is claiming that the divergence problem has been solved:
[The] solution is simple, elegant, and intuitive: global dimming. Since the 1960s—exactly when tree-ring data started to go awry—“there’s been large scale decreases in the amount of light that’s reaching the earth,” says Stine. It’s fairly easy to see why, too. In rapidly industrializing parts of the world with fewer emissions laws—like Southeast Asia—the light decline is particularly steep, and continues into the 21st century. On the other hand, in areas like the U.S. and Europe, you see a rapid decline in the middle of the 20th century, but then light levels steady themselves later on—right around the time most air pollution laws were put into place.
The article is largely the normal news magazine misrepresentation of Climategate and the scientific issues around temperature reconstructions and is not really worth the time of anyone other than the global warming faithful. However, the source of the alleged breakthrough is a paper by AR Stine and Peter Huybers, published in Nature Communications.
Annual growth ring variations in Arctic trees are often used to reconstruct surface temperature. In general, however, the growth of Arctic vegetation is limited both by temperature and light availability, suggesting that variations in atmospheric transmissivity may also influence tree-ring characteristics. Here we show that Arctic tree-ring density is sensitive to changes in light availability across two distinct phenomena: explosive volcanic eruptions (P<0.01) and the recent epoch of global dimming (P<0.01). In each case, the greatest response is found in the most light-limited regions of the Arctic. Essentially no late 20th century decline in tree-ring density relative to temperature is seen in the least light-limited regions of the Arctic. Consistent results follow from analysis of tree-ring width and from individually analysing each of seven tree species. Light availability thus appears an important control, opening the possibility for using tree rings to reconstruct historical changes in surface light intensity.
It seems that trees whose growth was said to be limited by temperature are actually sometimes limited by something else altogether.
This is one for Mr McIntyre, I fancy.